Priority is claimed on Japanese Patent Application No. 2005-123260, filed Apr. 21, 2005, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to: a planetary roller driving device including a planetary roller transmission mechanism which can control rotational speed ratio between an input axis and an output axis to a predetermined value centering on 1:1 and a steering apparatus including the same.
2. Description of the Related Art
In accordance with improvements in a vehicle performance, a recent steering apparatus for a vehicle has improvements in easiness and safety of handling operation. This kind of steering apparatus includes a power-assisting device which assists power required for handling operation along with changing shifted rotational speed of a steering handle corresponding to the vehicle speed.
A steering apparatus including a conventional planetary roller driving device disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-58896, changes shifted rotational speed of a steering handle by rotating inner gears of a planetary gear mechanism in the clockwise and in the counterclockwise using a speed-shifting motor. The inner gears are directly connected to a steering handle axis. In addition, this steering apparatus also enables maintaining constant rotational speed ratio by securing the inner gears using an electromagnetic plunger. Furthermore, by providing a power-assisting mechanism to a wheel steering rod, this steering apparatus controls the rotational-speed-controlling motor and the power assisting mechanism corresponding to the vehicle speed.
In addition, a conventional steering apparatus disclosed in Japanese Patent No. 2,949,604, has a construction of selectively driving and controlling a shifting speed variable mechanism and a power-assisting mechanism for a steering handle, using one driving motor and two electromagnetic clutches.
Furthermore, in a conventional steering apparatus disclosed in Japanese Unexamined Patent Application, First Publication No. 2001-30922, a planetary carrier of a planetary gear reduction mechanism having an input axis as a sun gear, is adopted as a reduction axis; and chain sprockets are fixed to the reduction axis. Through a chain engaged with the chain sprockets, a steering bar provided orthogonal to the reduction axis is moved left and right. The chain is guided by two idling sprockets which freely rotate around an axis of a rotational body which rotates around the reduction axis. And power-assisting for the steering bar is performed by rotational torque of the rotational body to which the idling sprockets are mounted and which is rotated by a motor. The steering apparatus has a construction of converting rotational movement to linear movement, and the construction enables deceleration of the moving steering bar at each rotational end side.
In a conventional steering apparatus disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-58896, a reduction device directly connected to a steering handle axis and a planetary gear mechanism become a noise source. In addition, since a power-assisting mechanism is separately mounted on a position of a steering bar, an engine room becomes tight. Furthermore, since the steering apparatus has many parts, manufacturing cost thereof is high.
In a conventional steering apparatus disclosed in Japanese Patent No. 2,949,604, since a steering speed variable mechanism and a power-assisting mechanism are selectively controlled by one driving motor and two electromagnetic clutches corresponding to the vehicle speed, the steering apparatus cannot use these mechanisms together at the same time.
The conventional steering apparatus disclosed in Japanese Unexamined Patent Application, First Publication No. 2001-30922, has a problem in that the reduction rate of the moving steering bar on the swinging end sides are constant and cannot be controlled. In addition, since the steering apparatus is provided at a position of a steering bar, an engine room becomes tight.
The present invention has an object of providing: a planetary roller driving device which enables easy installation thereof by combining a steering speed changing mechanism having low noise and directly connected to an axis such as a steering handle, and a power-assisting mechanism in a one body; and a steering apparatus including the planetary roller driving device.